1. Field of the Invention
This invention relates to the terminal structure of a flexible printed circuit board, wherein the terminal is ideal for connection to a miniaturized connector.
2. Description of the Prior Art
Electronic parts of a wide variety have recently been reduced in size and thickness, and this has been accompanied by the widespread use of flexible printed circuit boards designed to make effective utilization of available space. A flexible printed circuit board of this kind is obtained by forming electrically conductive patterns on a flexible insulating film.
In order to connect a flexible printed circuit board to the connector of an electronic part, a portion of one edge of a flexible printed circuit board 81 that is provided with electrically conductive patterns 82 is directly inserted into a connector, as illustrated in FIG. 9.
Since the flexible printed circuit board 81 consists of a thin film and exhibits flexibility, it has little strength. Therefore, in a case where the flexible printed circuit board 81 is directly inserted into a connector 90 (FIG. 10), a rigid resin base 86 for reinforcement is bonded to the underside of the flexible printed circuit board 81, as shown in FIG. 9.
The recent progress that has been made in miniaturizing devices has been accompanied by miniaturization of the connectors used to connect the flexible printed circuit board 81. In order to accommodate such miniaturized connectors, it is necessary to reduce the spacing between the electrically conductive patterns 82 shown in FIG. 9. With such an expedient, however, certain problems arise, which will now be described.
(1) In order to manufacture the flexible printed circuit board 81, the electrically conductive patterns 82 are formed on a large resin film by etching or screen printing, after which the resin film is subjected to cutting. As a result, a spacing .sup.l 1 of the electrically conductive patterns 82 can be rendered constant with good accuracy, as shown in FIG. 9, however, owing to a mechanical error which develops when the resin film is cut, a deviation is produced in spaces .sup.l 3, .sup.l 3 between both side edges of the flexible printed circuit board 81 and the outermost electrically conductive patterns 82 (that is, .sup.l 3.noteq..sup.l 3 is the result of the aforementioned mechanical error). When this deviation occurs in the spaces .sup.l 3, .sup.l 3 the electrically conductive patterns 82 cannot be accurately connected to the respective connection terminals inside the connector even if the flexible printed circuit board 81 is accurately inserted into the insertion hole of the connector. The more the spacing of the electrically conductive patterns 82 is narrowed, the more prominent this problem becomes. In certain cases, an electrically conductive pattern 82 which Is not intended to be connected may come into contact with a connection terminal inside the connector, thereby producing a short circuit.
(2) In order to smoothen the insertion of the flexible printed circuit board 81, a prescribed amount of play in the width direction is provided between the flexible printed circuit board 81 and the inner wall of the insertion hole of the connector. Consequently, when the flexible printed circuit board 81 is inserted into an insertion hole 91 of a connector 90, as illustrated in FIG. 10(a), there are cases where the flexible printed circuit board 81 fits into the insertion hole 91 askew at small angle .theta.. If the spacing .sup.l 1 (see FIG. 9) between the electrically conductive patterns 82 is small in such case, there is the danger that an electrically conductive pattern 82 which Is not intended to be connected may come into contact with a connection terminal inside the connector 90, thereby producing a short circuit.
(3) When the flexible printed circuit board is inserted into the insertion hole 91 of the connector 90, there are cases where the insertion of the flexible printed circuit board 81 into the insertion hole 91 stops midway, as shown in FIG. 10(b). In other words, since there is no indication on the flexible printed circuit board 81 by which the amount of insertion can be determined, it may be misconceived that the two are perfectly connected when in fact they are not, in which case the two would remain in an imperfectly connected state.